The main focus of this project was the nanoscale patterning of self-assembled
monolayers (SAMs) of alkanethiols on gold. This has involved continuing
development of scanning near-field photolithography (SNP) as a tool for
nanofabrication. SNP is a new technique that uses a scanning near-field optical
microscope (SNOM) coupled to a UV laser to create nanoscale structures. The
maximum resolution of conventional photolithography is 'AJ2 which is governed by
the diffraction limit, SNOM can improve this by using a small aperture (50 nm) and
holding the probe very close to the sample (10-15 run), thus limiting diffraction. SNP
uses this to create features much smaller than the diffraction limit for 244 run light to
the order ofA/30 or 9 run.
The majority of this work has been on SAMs of alkanethiols on gold, but also
alkanethiols on palladium have been used. These basic systems have been studied by
various surface science techniques such as contact angle goniometry, atomic force
microscopy (AFM), friction force microscopy, X-ray photoelectron spectroscopy, and
also surface plasmon resonance to study protein attachment. The attachment of
biological molecules was examined by either organic reactions on the surface and
photochemical attachment. These were subsequently patterned using micronscale
photolithography and SNP.
Photolithography of SAMs used UV light to perform photooxidation of surface bound
alkanethiols, converting them to alkylsulfonates. Alkylsulfonates are weakly bound
to the surface and can be replaced by an opposing thiol and therefore make a
bifunctional pattern. This can be used for micronscale patterns. These were also used
to pattern biological structures and for the study of alkanethiols as etch resists to a
novel etchant (mercaptoethylamine). Using mercaptoethylamine etchant with SNP
allowed the fabrication of extremely small structures using a high scanning speed on
the SNOM.